SCP-XXXX appears to be a black rotary dial telephone with a lobster as the telephone's handle.

I come across this a lot, but don't use 'seems to' or 'appears to be' unless the effect or object actually isn't what it seems like.

SCP-XXXX was found at Museum für Kommunikation Frankfurt, 5/██/1996.

Why would you only censor the month?

SCP-XXXX-1 will begin to change in appearance and become animated.

Will animate*

The known way to activate SCP-XXXX is to interact with SCP-XXXX.

Yes, you just explained this.

5 minutes: Subject will vanish, no traces can be found. The lobster handle would remain levitating in the air without anything supporting it. Footsteps can be heard, but the origin of the sounds is unknown.

Right now, you have an object with a clearly defined activation and function, with no context or backstory, essentially a generic magic object. I recommend adding some more to this, because at this point the idea seems to be more of an entry on the log of anomalous items than an SCP object that would merit special Foundation containment.

If you're set on going with this as a concept, I would either add to the effect (make it more interesting than just vanishing) or add to the context of the creation of the SCP itself.

Some aspects people like to add into the SCP to give the reader more to think about include answers to questions like

- Why does it exist? Does it have a purpose?
- What might the intentions of the creator have been?
- Why does it act the way it does?